Filtering noise from a wire

[Demon]

I have install pushbuttons on the flip side of these (5V circuit), and the button state is sent via a 3rd wire to another board along with the VDD and VSS wires:




What is the proper technique to filter noise picked up by the wires before the signal is processed by a MCP23017 I/O Expander?


I searched here and google for "decouple wire lines", but it's too vague of a question. And I don't know how I can state it better, or differently.


I've read about ferrite beads, but I'm not sure if capacitors could do the job as well. I remember hacking a keyboard many moons ago, and it had aluminium foil along the back cover.


EDIT: I have to consider that someone might have speakers, cell phones or other "noisy" devices placed right beside the unit.